1. Field of the Invention
The present invention relates to an argon ion laser tube, and more particularly to an argon ion laser tube in which misalignment of constituent mirrors caused upon the tube being energized and disenergized is reduced and hence an output characteristic is stabilized.
2. Description of the Prior Art
A prior art argon ion laser tube comprises, as illustrated in FIG. 1, an anode 1 and a hot cathode 2 both serving as electrical discharge electrodes, a laser tube 3 for exciting laser medium argon molecules, a heat radiating plate 4 for radiating much heat produced in the laser tube 3, a cathode bulb 5 serving as an enclosure for enclosing the hot cathode 2 and also serving as a supporter for a gas tank and a total reflection mirror 6b, a semitransparent mirror 6a and a total reflection mirror 6b both constituting an optical resonator, a hot cathode introduction bar 20 serving to supply power to the hot cathode 2 and to connect an electrical discharge current to the outside, and an insulator 21 for electrically insulating the hot cathode introduction bar 20 and the cathode bulb 5. The argon ion laser tube is mounted on a laser oscillator in the same manner as an argon ion laser tube of an embodiment of the present invention illustrated in FIG. 2.
Operation of the prior art argon ion laser tube is as follows.
Referring again to FIGS. 1 and 2, electrical discharge is produced between the anode 1 and the hot cathode 2 to excite argon molecules in the laser tube. Laser oscillation and light amplification is achieved in the optical resonator composed of the semitransparent mirror 6a and the total reflection mirror 6b. A laser output is derived from the semitransparent mirror 6a. Thereupon, the laser tube 3 produces much heat owing to the electrical discharge, most part of which is freed from the heat radiating plate 4 to the outside and part of which is transmitted to the cathode bulb 5.
The prior art argon ion laser tube described above however has a drawback: there is produced temperature differences among the various portions on the cathode bulb 5 depending upon the amount of heat transmitted to the cathode bulb 5 and upon air flows directed from an air cooling fan mounted on the laser oscillator to cause misalignment of the total reflection mirror 6b supported on the cathode bulb 5. In particular, upon excitation of the argon ion laser tube from its cooled state misalignment of the mirrors is very severe because of temperature distribution upon operation being quite different from that upon the non-operation, so that the output of the laser immediately after the initiation of the electrical discharge is started at a severely lower value than in the operation and gradually approaches the output at the operation.